The world owes much of its cultural legacy to Constantinople’s walls. When Constantinople was under seige by neighboring enemies, the Roman city’s elaborate system of moats, outer walls, and inner walls stood tall. Surviving numerous fire attacks, the walls were eventually brought down by more modern tools of warfare, but, thankfully, classical culture survived.

Excerpt: The most important walls in western history aren’t even in the West. They surround the modern city of Istanbul, Constantinople as the Romans called it. And for a thousand years, the fate of Europe depended on them.

Constantinople was designed to be the center of the world. When the frontiers of the Roman Empire began to crumble in the 4th Century, the capital was moved to the cultured, wealthy, and still stable East. There, at the crossroads between Europe and Asia, the hub of the major trade routes of the ancient world, the Emperor Constantine built his city.

This was the city of libraries and universities, 20 times the size of London or Paris at the time. It contained the priceless knowledge of the classical world which was fading in the West.

To protect this masterpiece from its many enemies, Constantine’s successors built the finest defensive fortifications ever made. The first line of protection was a moat 60 feet wide and 22 feet deep, stretching all four miles from coast to coast. Pipes from inside the city could fill it at the first sight of the enemy, and a short wall protected archers who could fire at the soaked soldiers trying to swim across.

Those who were lucky enough to clear the moat had to contend with an unceasing barrage from the 27 foot outer wall above. Arrows, spears, or far worse, Greek fire — an ancient form of napalm that would ignite on contact and couldn’t be extinguished by water — would rain down on them.